I love GTK2, but I can do without GTK3, seeing we're at 3.22 and it's still not as stable or regression free as GTK2.

I'd be the first to build and use a Firefox where the Qt port was updated and made to work but GTK is the GUI toolkit used by Firefox outside Android, macOS and Windows. That said, GTK2 was and still is very good at what it does. It just works but doesn't support Wayland.

I cannot move to Wayland anyway until xterm or rxvt-unicode are ported since XWayland integration is still imperfect. Like they wrote in the bug report, while GTK2 doesn't have a Wayland backend, GTK3's backend isn't really production quality either with dialogs sometimes opting to zoom out rather than scale out or general stability issues. If you try to start Firefox under Wayland by telling GDK to use Wayland, it just crashes on startup.